Mobile radio antennas for base stations normally have a vertically running conductive reflector which may possibly also be provided with webs, edge boundaries etc. which run in the longitudinal or vertical direction and are offset outwards from the center, and which extend such that they run at right angles to the reflector plane or at an angle to it. Two or more antenna elements or antenna element groups which are offset in the vertical direction are generally arranged in front of the reflector and, for example, can transmit and/or receive in one polarization or else in two mutually perpendicular polarizations.
The dual-polarized antenna elements are frequently aligned at angles of +45° and −45° to the vertical (and to the horizontal), so that they are also referred to as X-polarization antenna elements.
The antenna elements and antenna element groups may be arranged alongside one another in one or more columns. Antenna arrays such as these which comprise two or more columns alongside one another generally, however, likewise have a common reflector or a common reflector plate.
All feasible antenna elements may be used as the antenna elements, for example single-polarized or dual-polarized antenna elements, dipole antenna elements or dipole-like antenna elements, patch antenna elements etc. With regard to the various antenna element types that are used, reference is made merely by way of example to the following prior publications, specifically DE 197 22 742 A1, DE 196 27 015 A1, U.S. Pat. No. 5,710,569, WO 00/39894 or DE 101 50 150 A1.
Antenna arrangements such as these are normally accommodated in a radome which is used to protect the antenna elements against weather influences. The radome itself allows electromagnetic waves to pass through it and is generally composed of a glass-fiber-reinforced plastic.
Although mobile radio antennas can be designed such that the radome, which is similar to a housing, has a front face which is in the form of a shell and which can be fitted to the antennas and to the baseplate which covers the reflector, a radome is also frequently used which is closed in the circumferential direction and is open on its opposite end faces, where it can be closed by fitting terminating caps which are composed of glass-fiber-reinforced plastic or else, for example, of metal. The appropriate electrical connections for the feed lines as well as further measures, for example for adjusting the downtilt angle, etc., are also provided on the connecting cap located at the bottom. These electrical connections may, however, also be provided on the rear face of the radome, that is to say at the rear on the radome. Finally, appropriate holding and fixing devices are also provided, via which the entire antenna is, for example, held and fixed on a mast. These holding and fixing devices are generally provided on the respective load-bearing parts of the structure, for example on the reflector, on the radome itself, etc.
It is known for mobile radio antennas to generally be designed to transmit only in one specific sector, for example for a sector of 120°, ±30° or 180°±30°, etc. A high back-to-front ratio is thus frequently desirable, which should be greater than 20 dB, and frequently even greater than 25 dB, or even greater than 30 dB.
In order to achieve a better back-to-front ratio, an additional metal sheet can already be fitted at a distance behind the rear face of the radome in the case of a mobile radio antenna which is accommodated in a radome (in which case the entire antenna device including the reflector as well as the antenna elements or antenna element groups which are formed on it is accommodated in the radome, which is closed in the circumferential direction). This effectively results in a “double reflector”, thus improving the back-to-front ratio.
Attempts have already been made not to install this second reflector separately at a distance behind the radome but to apply to the rearward face of the radome itself, or the inner face of the radome.
The technology herein provides an improved exemplary illustrative non-limiting radome in particular for a mobile radio antenna, as well as an associated mobile radio antenna, whose design is simple and efficient and which has optimum electrical characteristics.
The exemplary illustrative radome is distinguished by flat line structures being incorporated in the material of the radome itself. Thus, in other words, flat line structures are incorporated in the material of the radome itself during the radome production process, and generally cannot be seen at all from the outside. If, by way of example, a large-area line structure is incorporated in the rearward wall of a radome such as this which, for example, is composed of glass-fiber-reinforced plastic, then a reflector can be formed in this way. The reflector itself cannot be seen from the outside unless the rearward wall of the radome is drilled open or external material layers of the radome were to be removed.
A reflector such as this need neither be produced separately nor be fitted and installed separately. It is integrated in the radome itself.
These large-area conductive structures may, however, be incorporated not only on the rearward wall but, in some cases, also in the side wall areas (which in general also run vertically when the antenna is installed with the radome aligned vertically), so that, by way of example, side outer webs or edge boundaries are formed, such as those which are also known per se for reflectors which are manufactured separately from metal sheets.
Finally, flat line structures such as these could, however, even be accommodated on a different face in the radome, for example even in the front face. This would make it possible, for example, to form passive or else active line patches which are located, in particular, above antenna elements formed from patch antennas. In the case of an active patch, the patch may be stimulated as an antenna element, for example by means of an aperture coupling. This is normally done using a printed circuit which contains a feed network above a ground plane. The ground plane has a slot (aperture) which is stimulated by the feed network. This slot is then coupled to the patch. No conductive connection to the patch is required with this type of patch feed.
The flat line structures may be produced in widely differing ways. These flat line structures may, for example, have a hole structure or a grating structure. They may be composed of conductor tracks running in the longitudinal direction, or else conductor tracks running transversely, particularly when these conductor tracks are connected via non-conductive cable structures running in the longitudinal direction. In an exemplary illustrative non-limiting implementation there are no restrictions to a specific structure or to a specific material. When grating or hole structures are used, only the mesh, grating or hole size should be designed appropriately such that it is suitable for the corresponding waveband of the mobile radio antenna. In other words, the hole size of such a hole or grating structure should therefore be smaller than λ/10, when λ represents the wavelength of the highest transmitted frequency.
In one exemplary illustrative non-limiting implementation, the flat line structure to be incorporated may be composed of metal, for example aluminum or an aluminum foil, which is coated in the factory itself on both sides with paper or a material which includes paper. Such coated metal foils or, in particular, aluminum foils are commercially available and can be incorporated particularly well in a radome during production, since the outer layers of the metal foil, which are composed of paper or include paper, can be impregnated with resin particularly well so that a particularly good connection of a flat line structure such as this can be incorporated in a radome which is composed of plastic, in particular glass-fiber-reinforced plastic.
A radome such as this is preferably also used for omnidirectional antenna elements which, for example, can be held via the end caps which are placed on the radome. This allows an omnidirectional antenna element to be used to produce a corresponding directional antenna element, in which case the 3 dB beamwidth of the antenna is defined by the size of the flat line structure incorporated in the radome and by the reflector formed in this way.
A radome such as this forming an incorporated reflector can be used to improve the back-to-front ratio.
This is because the use of a radome such as this for a mobile radio antenna with a separate reflector on which the antenna elements and antenna element structures are formed effectively results in a double reflector.
The exemplary illustrative radome thus has a large number of advantages. In comparison to conventional solutions, the exemplary illustrative solution with a reflector incorporated in the radome material leads to the radome being lighter overall, to the incorporated reflector being better protected, and the entire radome arrangement thus also becoming denser (because, for example, there is no need to fit an additional reflector and install an additional reflector on the inside or outside of the radome). In particular, when additional reflector devices such as these were adhesively bonded to the radome material in the prior art, there was also a risk of them becoming detached from the radome material again when these reflectors were subjected to a large amount of heat. Finally, this also avoids the creation of intermodulation products. Furthermore, the total number of components required is also reduced, and the overall assembly complexity is simplified and reduced.